The study of phage-host interactions and their influence on toxinogeny in Corynebacterium diphteriae will be extended. Using phage and host mutants the control and regulation of toxin synthesis will be studied. The genetics of converting phages and non-converting phages will also be studied with particular emphasis on the relationship of the prophage map to the vegetative phage map. Converting and non-converting phages will be compared, particularly the extent to which they may share the tox gene, and the relationship between their phage immunity activity. Extensive study of lysogeny, its establishment, maintenance and description is projected in association with the latter project. The relationship of the molecular and cellular data to the natural history of C. diphtheriae will be explored with stress on those factors affecting the balance between toxinogenic and non-toxinogenic strains of C. diphtheriae. This latter study is expected to shed light on factors affecting the epidemiology of diphtheria.